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WBG Devices in Electrical Motor Drives
NOVEL POWER SYSTEMS ENABLED BY WIDE BAND-GAP SEMICONDUCTORS WORKSHOP
Vladimir Blasko, UTRCSeptember 13, 2016
Washington DC
2
Opportunities, Grand Challenge for New Topologies
• Green drive with sinusoidal input and output• EMI and PWM issues contained within the drive• Utilization of parasitics to facilitate main functions• Greater use of semiconductors on the expense of
passives• Active filtering• Losses reduced by factor of 2• Size and weight reduced by 2• Same cost and life time
Figure of Merits, Grand Challenge and GapsPerformance Indices Have different weights for different applications,
two examples below:(A) Aerospace and high end drives:• Power per weight [kW/kg], 10 kW/kg• Power density [kW/dm3], 10 kW/dm3
• Relative cost [kW/$]• Relative losses [%], <2%• Life time [Years], >10Y• EMI – no external filters or shielded cables• Voltage THD: better than for 3 level
inverter(B) Commercial drives:Relative losses, <2%• Life time 5 to 10Y• No external filters for EMI or dv/dt• Low grid harmonics (IEEE 519)• Low cost
GapsPackaging/integration • Packaging infrastructure for ultra high speed devices
missing• Take benefits of parasitics• 3D packaging• Multi physics integration tools
• Life time issues for high temperature operation (thermal cycling, power cycling mostly unknown)
WBG device driven power converter topologies • Low PWM frequency (1 to 20kHz)• Highly polluted V/I output of the drive
• The drive topologies we work on today should anticipate device performance and cost we expect in the future based on the performance trends for devices
• Focus on system level benefits
Effects of PWMHigh speed switching has negative effects on the motor and the system
3
System level effects• EMI conductive and radiated• Noise in electrical circuits
Effects on the motor• DM current ripple
• Additional Cu losses• Additional Fe losses• Winding overvoltages and partial
discharge• CM currents
• Bearing current
agv
bgv
cgv
cmv
,...2
,6
)(31
dcdc
cgbgagcm
VV
vvvv
±±=
++=
ci
vdtdv
ai
bi
ci
dtdiLv a
a =
MOTOR
CABLE
DRIVESOURCE
Drive is a generator of voltage waveforms with sharp transitions between (high) voltage levels
MOTORDRIVESOURCE FilterFilter
CABLE
Electromagnetic interference (EMI)
4
EMI is a disturbance generated by an external source that affects the operation of a sensitive electrical circuit.
EMI standards define the regulated frequency range and corresponding emission limit for products in various applications. Impact on cost.
In the context of power electronics, EMI is the high frequency voltage and current components generated by power converters
EMI: Radiated and ConductedConducted EMI:• Differential Mode (DM)-Only flows on the
power leads• Common Mode (CM)-Flows to the ground.• CM EMI is very important for qualifications
of power electronic converters• PWM switching frequency, Si Devices
• 10 to 20kHz P<5kW• 2 to 10kHz 5kW<P<300kW• <2kHz P>300kW
• WBG devices fpwm < 50KHz
Mitigation for CM EMI• Shielded cables/conduits between motor and drive• EMI filters at line side of the drive• RLC filters at the output of the drive• Different PWM techniques to reduce CM voltage• Active CM filter• Good lay out of the drive• Conductive/shielding enclosure for radiated EMI• Integrated motor drive solutions
Input line filter• Increases impedance between
source and drive
Output motor filter• Softens voltage transitions • Increases HF impedance
between motor and driveCable• Shielding for radiated emi• Low impedance return path for
ground currents
Over-voltages and Bearing CurrentsCause of winding isolation and bearing failures
5
High switching speed with high dV/dt and transmission line effects/overvoltage on the motor terminals, isolation failure dv/dt>600V/us acceptable level – bipolar technology, Partial discharge and motor winding failure, need for inverter
grade wire For IGBT based technology start to play role for cables >10m,
with increased speed of semiconductor switches (x10) shorter distances >1m will start to play critical role
Mitigation techniques: Output filters (RLC) to slow voltage transition speed,
preferred option for smaller power (usually simple filters like just inductor will be sufficient)
Motor terminator (to match impedance, close to motor winding, preferred option for larger motors)
Reinforced isolation on first turn on the motor winding Slowdown switching devices (fpwm~5kHz) Multi level inverters (reduced voltage steps)
Bearing currents • Cause of bearings failure• Mitigation: filters, ceramic bearings, shaft
grounding, closed winding slots
MOTORDRIVESOURCE FilterFilter
CABLE
Terminator
cmv
w fC3
wrC
rfC bCframe
High frequency equivalent circuit with
main capacitances important for bearing
currents
6
Existing drive topologies – comparisonPresent topologies are dominated by hard switching voltage source variants without considerations for PWM and EMI issues
R
S
T
S1
S2
S3
Cdc
Cdc
Vienna Rectifier
Input Inductors
DC
Link
RS
T
CSIConverter
CSIConverter
DC Link Inductor MOTOR
R
ST
IGBTInverter
IGBTConverter
DCLinkCAP
MOTOR
R
S
T
InputFilter
OV Protection
Matrix Converter
MOTOR
Vdc/2
Vdc
LOW FREQUENCY SWITCHING
HIGH FREQUENCY SWITCHING
2 level 3 level 4 leg NC Vienna Cascaded
CSI
Back to Back VSC
MxC
Common Mode Tr.
ABC
+Vdc/2
-Vdc/2
0
ABC
IGBTInverterZ Link
“Z” source
Resonant 2 Level Multi Level
Multi level
cascadedVienna
Back to Back VSC
CSI Mxc Z
Overall Complexity# of Power componentsRevers blocking devicesAdditionala passive components to meet EMI
Gate driving
Power input complexity
Control Complexitydv/dt and dI/dtConduction lossesSwitching lossesExtra Voltage or Current stressTHDRegeneration
Wide Band Gap Power DevicesDevices and applications – historic perspective
7
Transition from BJT to IGBT technology
Fast transition • 1988/89 IGBT lab samples available• 1991 – Drives with IGBTs available
Packaging/integration • Packaging infrastructure was available (all
Si based)• Life time issues (thermal cycling, power
cycling mostly unknown)
Device driven power converter topologies
• Low voltage 6 step (VSI vs CSI)• Multi level inverters• Cascaded inverters
Transition from Si to SiC /GaN technology
Slow transition• Cost of active/switching devices• Need for new packaging infrastructure to support
high temperature operation • Thermal/power cycling• High temperature passive devices and control
Packaging/integration • Need for material and test data to guarantee long
life time• Multi physics integration tools
New power converter topologies• Integrated filters (green drives/inverters) with
sinusoidal outputs, HF – enabler)• Broader application of multi level, cascaded and
CSI inverters (enabled by low conduction losses and HF)
• Reduced size and weight, simplified cooling